rust/tests/ui/proc-macro/auxiliary/attr-args.rs

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// force-host
// no-prefer-dynamic
rustc: Stabilize much of the `proc_macro` feature This commit stabilizes some of the `proc_macro` language feature as well as a number of APIs in the `proc_macro` crate as [previously discussed][1]. This means that on stable Rust you can now define custom procedural macros which operate as attributes attached to items or `macro_rules!`-like bang-style invocations. This extends the suite of currently stable procedural macros, custom derives, with custom attributes and custom bang macros. Note though that despite the stabilization in this commit procedural macros are still not usable on stable Rust. To stabilize that we'll need to stabilize at least part of the `use_extern_macros` feature. Currently you can define a procedural macro attribute but you can't import it to call it! A summary of the changes made in this PR (as well as the various consequences) is: * The `proc_macro` language and library features are now stable. * Other APIs not stabilized in the `proc_macro` crate are now named under a different feature, such as `proc_macro_diagnostic` or `proc_macro_span`. * A few checks in resolution for `proc_macro` being enabled have switched over to `use_extern_macros` being enabled. This means that code using `#![feature(proc_macro)]` today will likely need to move to `#![feature(use_extern_macros)]`. It's intended that this PR, once landed, will be followed up with an attempt to stabilize a small slice of `use_extern_macros` just for procedural macros to make this feature 100% usable on stable. [1]: https://internals.rust-lang.org/t/help-stabilize-a-subset-of-macros-2-0/7252
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#![crate_type = "proc-macro"]
extern crate proc_macro;
use proc_macro::TokenStream;
#[proc_macro_attribute]
pub fn attr_with_args(args: TokenStream, input: TokenStream) -> TokenStream {
let args = args.to_string();
rustc: Tweak custom attribute capabilities This commit starts to lay some groundwork for the stabilization of custom attribute invocations and general procedural macros. It applies a number of changes discussed on [internals] as well as a [recent issue][issue], namely: * The path used to specify a custom attribute must be of length one and cannot be a global path. This'll help future-proof us against any ambiguities and give us more time to settle the precise syntax. In the meantime though a bare identifier can be used and imported to invoke a custom attribute macro. A new feature gate, `proc_macro_path_invoc`, was added to gate multi-segment paths and absolute paths. * The set of items which can be annotated by a custom procedural attribute has been restricted. Statements, expressions, and modules are disallowed behind two new feature gates: `proc_macro_expr` and `proc_macro_mod`. * The input to procedural macro attributes has been restricted and adjusted. Today an invocation like `#[foo(bar)]` will receive `(bar)` as the input token stream, but after this PR it will only receive `bar` (the delimiters were removed). Invocations like `#[foo]` are still allowed and will be invoked in the same way as `#[foo()]`. This is a **breaking change** for all nightly users as the syntax coming in to procedural macros will be tweaked slightly. * Procedural macros (`foo!()` style) can only be expanded to item-like items by default. A separate feature gate, `proc_macro_non_items`, is required to expand to items like expressions, statements, etc. Closes #50038 [internals]: https://internals.rust-lang.org/t/help-stabilize-a-subset-of-macros-2-0/7252 [issue]: https://github.com/rust-lang/rust/issues/50038
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assert_eq!(args, r#"text = "Hello, world!""#);
let input = input.to_string();
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assert_eq!(input, "fn foo() {}");
r#"
fn foo() -> &'static str { "Hello, world!" }
"#.parse().unwrap()
}
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#[proc_macro_attribute]
pub fn identity(attr_args: TokenStream, _: TokenStream) -> TokenStream {
attr_args
}